The invention relates to ion texturing methods and articles.
Multi-layer articles can be used in a variety of applications. For example, superconductors, including oxide superconductors, can be formed of multi-layer articles. Typically, such superconductors include a layer of superconductor material and a layer, commonly referred to as a substrate, that can enhance the mechanical strength of the multi-layer article.
Generally, in addition to enhancing the strength of the multi-layer superconductor, the substrate should exhibit certain other properties. For example, the substrate should have a low Curie temperature so that the substrate is not ferromagnetic at the superconductor""s application temperature. Furthermore, chemical species within the substrate should not be able to diffuse into the layer of superconductor material, and the coefficient of thermal expansion of the substrate should be about the same as the superconductor material. Moreover, if the substrate is used for an oxide superconductor, the substrate material should be relatively resistant to oxidation.
For some materials, such as yttrium-barium-copper-oxide (YBCO), the ability of the material to provide high transport current in its superconducting state depends upon the crystallographic orientation of the material. For example, such a material can exhibit a relatively high critical current density (Jc) when the surface of the material is biaxially textured.
As used herein, xe2x80x9cbiaxially texturedxe2x80x9d refers to a surface for which the crystal grains are in close alignment with a direction in the plane of the surface or in close alignment with both a direction in the plane of the surface and a direction perpendicular to the surface. One type of biaxially textured surface is a cube textured surface, in which the primary cubic axes of the crystal grains are in close alignment with a direction perpendicular to the surface and with the direction in the plane of the surface. Examples of cube textured surfaces include the (100)[001] and (100)[011] surfaces, and an example of a biaxially textured surface is the (113)[211] surface.
For certain multi-layer superconductors, the layer of superconductor material is an epitaxial layer. As used herein, xe2x80x9cepitaxial layerxe2x80x9d refers to a layer of material whose crystallographic orientation is derived from the crystallographic orientation of the surface of a layer of material onto which the epitaxial layer is deposited. For example, for a multi-layer superconductor having an epitaxial layer of superconductor material deposited onto a substrate, the crystallographic orientation of the layer of superconductor material is derived from the crystallographic orientation of the substrate. Thus, in addition to the above discussed properties of a substrate, it can be also desirable for a substrate to have a biaxially textured surface or a cube textured surface.
Some substrates do not readily exhibit all the above-noted features, so one or more intermediate layers, commonly referred to as buffer layers, can be disposed between the substrate and the superconductor layer. The buffer layer(s) can be more resistant to oxidation than the substrate, and reduce the diffusion of chemical species between the substrate and the superconductor layer. Moreover, the buffer layer(s) can have a coefficient of thermal expansion that is well matched with the superconductor material.
In some instance, a buffer layer is an epitaxial layer, so its crystallographic orientation is derived from the crystallographic orientation of the surface onto which the buffer layer is deposited. For example, in a multi-layer superconductor having a substrate, an epitaxial buffer layer and an epitaxial layer of superconductor material, the crystallographic orientation of the surface of the buffer layer is derived from the crystallographic orientation of the surface of the substrate, and the crystallographic orientation of the layer of superconductor material is derived from the crystallographic orientation of the surface of the buffer layer. Therefore, the superconducting properties exhibited by a multi-layer superconductor having a buffer layer can depend upon the crystallographic orientation of the buffer layer surface.
In certain instances, a buffer layer is not an epitaxial layer but can be formed using ion beam assisted deposition. Typically, ion beam assisted deposition involves exposing a surface to ions directed at a specific angle relative to the surface while simultaneously depositing a material. In instances where ion beam assisted deposition is used to form a buffer layer, the crystallographic orientation of the surface of the buffer layer can be unrelated to the crystallographic orientation of the surface of the underlying layer (e.g., a substrate). Generally, however, the ion beam deposition parameters such as, for example, the ion energy and beam current, the temperature, the ratio of the number of atoms arriving at the surface relative to the number of ions coincidentally arriving at the surface, and the angle of incidence on the surface are selected so that the crystallographic orientation of the surface of the buffer layer provides an appropriate template for a layer that is deposited on the surface of the buffer layer (e.g., a layer of superconducting material).
The invention generally relates to ion texturing methods and articles.
In part, the invention relates to the realization that, by selecting the appropriate combination of parameters, multiple ion beams (e.g., two, three, four, etc.) can be used to increase the degree of texture of the surface (e.g, a noncrystalline surface) of a layer of material (e.g., a layer of an already deposited material, such as an already deposited buffer layer) so that the surface of the material has a predetermined crystallographic orientation. The crystallographic orientation of the ion textured surface can be different than the natural growth orientation of the layer of material.
The surface to be textured can be, for example, that of a substrate, a buffer layer, a protective layer or a layer of superconductor material. In certain embodiments, a multi-layer article (e.g., a multi-layer superconductor article, such as a coated superconductor article) can include more than one layer having an ion textured (or at least partially ion textured surface).
Materials that can be ion textured include, for example, metals, alloys, oxides of metals, nitrides of metals, oxides of alloys and nitrides of alloys. Such materials include, for example, nickel, nickel alloys, silver, MgO, titanium nitride, zirconia, zirconium nitride, TbOx, GaOx, ceria (CeO2), yttria stabilized zirconia (YSZ), Y2O3, LaAlO3, SrTiO3, Gd2O3, LaNiO3, LaCuO3, SrRuO3, NdGaO3, ruthenium oxide, barium titanate, lanthanum gallate, indium oxide and NdAlO3.
In some embodiments, the combination of appropriate parameters (e.g., the angle of the ion beams relative to the surface normal, the angle of the ion guns relative to each other and/or the crystal structure of the layer of material exposed to the ion beams) can be used to provide the predetermined crystallographic orientation of the surface in a relatively short period of time.
The multiple ion beams can be simultaneously active, or the multiple ion beams can be used in sequence. In some embodimnents, some or all of the ion beams can be simultaneously active for a portion of the ion bombardment, and some or all of the ion beams can be used sequentially for a portion of the ion bombardment.
In some embodiments, the multiple ion beams can provide an ion flux sufficiently high so that the sputtering rate of the noncrystalline surface would exceed the atom arrival rate during certain vapor deposition processes.
In certain embodiments, the process can provide a noncrystalline substrate having an ion textured surface.
In some embodiments, the process can provide a substrate with a noncrystalline layer deposited thereon. The surface of the noncrystalline layer can be ion textured.
In certain embodiments, the process can provide a substrate with one or more buffer layers (crystalline or noncrystalline, and/or epitaxial or nonepitaxial) with a layer (e.g., a thin protective layer) deposited thereon. The surface of the layer (e.g., protective layer) can be ion textured. The layer can act as a protective layer for one or more (e.g., all) of the underlying layers. The layer can be chemically compatible with a superconductor material or a precursor thereof (e.g., chemically compatible with a halogen-containing precursor of YBCO, such as a fluoride-containing precursor, including one or more BaF2-containing precursors).
In one aspect, the invention features a method of ion texturing a noncrystalline surface of a layer of a cubic structure material. The method includes exposing the noncrystalline surface to at least two ion beams to texture the noncrystalline surface and form a biaxially textured surface of the cubic structure material. The at least two ion beams impinge on the surface of the noncrystalline layer at a first angle relative to a perpendicular to the noncrystalline surface, the at least two ion beams being disposed relative to each other at a second angle around the perpendicular to the noncrystalline surface. The second angle is about 90xc2x0 and so that a crystal plane of the biaxially textured surface is oriented perpendicular to the biaxially textured surface.
The cubic structure material can be YSZ, and the first angle can be from about 51xc2x0 to about 59xc2x0 (e.g., about 55xc2x0).
The cubic structure material can be YSZ, and the YSZ can be at a temperature of from about room temperature to about 900xc2x0 C. during ion texturing.
The cubic structure material can be, for example, a rock-salt structure material or a fluorite structure material.
The cubic structure material can be, for example, MgO, TiN, CaO, SrO, ZrO, BaO, YSZ or ceria.
The second angle can be about 180xc2x0.
The second angle can be about 90xc2x0.
The method can further include disposing a layer of a second material on the biaxially textured surface of the cubic structure material. The second material can be, for example, a superconductor material, a precursor of a superconductor material, a material that is chemically compatible with a superconductor material, or a material that is chemically compatible with a precursor of a superconductor material.
The second material can be chemically compatible with BaF2.
The second material can be, for example, ceria, LaAlO3 or SrTiO3.
The second material can be, for example, YBCO or a precursor of YBCO.
The biaxially textured surface of the cubic structure material can be cube textured.
The method can further include, before exposing the noncrystalline surface to the at least two ion beams, forming the layer of the cubic structure material having the noncrystalline surface by simultaneously depositing the cubic material and exposing the cubic material to at least one ion beam.
The method can further include, after forming the biaxially textured surface, simultaneously depositing more of the cubic material on the biaxially textured surface and exposing the cubic material to at least one ion beam.
The at least two ion beams can simultaneously impinge on the noncrystalline surface.
The at least two ion beams can impinge on the noncrystalline surface in sequence.
The at least two ion beams can be, for example, two ion beams, three ion beams or four ion beams.
In another aspect, the invention features a method of ion texturing a noncrystalline surface of a layer of a material. The method includes exposing the noncrystalline surface to at least two ion beams to texture the noncrystalline surface and form a textured surface of the material. The first ion beam of the at least two ion beams impinges on the surface at a first angle relative to the perpendicular to the noncrystalline surface. The second ion beam of the at least two ion beams impinges on the surface of the noncrystalline layer at a second angle relative to a perpendicular to the noncrystalline surface. The at least two ion beams are disposed relative to each other at a third angle so that a crystal plane of the biaxially textured surface is oriented perpendicular to the biaxially textured surface.
The at least two ion beams can be, for example, two ion beams, three ion beams or four ion beams.
The at least two ion beams can simultaneously impinge on the noncrystalline surface.
The at least two ion beams can impinge on the noncrystalline surface in sequence.
The method can further include, before exposing the noncrystalline surface to the at least two ion beams, forming the layer of the material having the noncrystalline surface by simultaneously depositing the material and exposing the material to at least one ion beam.
The method can further include, after forming the biaxially textured surface, simultaneously depositing more of the material on the textured surface and exposing the material to at least one ion beam.
The method can further include disposing a layer of a second material on the textured surface of the material. The second material can be, for example, a superconductor material, a precursor of a superconductor material, a material that is chemically compatible with a superconductor material, and a material that is chemically compatible with a precursor of a superconductor material.
The second material can be chemically compatible with BaF2.
The second material can be, for example, ceria, LaAlO3 or SrTiO3.
The second material can be, for example, YBCO or a precursor of YBCO.
The material can be at an exposure temperature during exposure to the at least two ion beams with the exposure temperature being less than a crystallization temperature of the material.
The textured surface can be biaxially textured.
The textured surface can be cube textured.
The material can be, for example, a cubic structure material or a hexagonal structure material.
The material can be a rock salt structure material or a fluorite structure material.
The ion flux at the surface of the material can be at least about 10 microAmperes per square centimeter.
The crystal plane can be the (001) plane.
The method can texture the material to a depth of less than about 50 nanometers.
The textured surface can have a X-ray phi scan full width at half maximum of less than about 20xc2x0.
The textured surface can have a root mean square roughness of less than about 100 angstroms.
The noncrystalline layer can be supported by a substrate. The substrate can be a nontextured substrate.
The method can be performed in a pressure of less than about 10 millitorr.
The exposure to the ions can occur for a time period of at least about 10 seconds.
The method can further include, after an initial ion exposure, decreasing the temperature while exposing the surface to ions.
The first angle can be different than the second angle.
In a further aspect, the invention features a method that includes exposing a surface of a noncrystalline layer of a first material to at least two ion beams to texture the noncrystalline surface and to form a textured surface of the first material. The method also includes disposing a layer of a second material on the textured surface of the first material. The second material is chemically compatible with a third material. The third material is a superconductor or a precursor of a superconductor.
The third material can be, for example, a rare earth metal oxide superconductor or a precursor of a rare earth metal oxide superconductor.
The third material can be, for example, YBCO or a precursor of YBCO.
The third material can be an acid (e.g., a halogenated acetic acid, such as trifluoroacetic acid).
The third material can contain BaF2.
The method can form a superconductor article having a critical current density of at least about 5xc3x97105 Amperes per square centimeter.
The second material can be, for example, ceria, LaAlO3 or SrTiO3.
The first material can be, for example, YSZ or a nitride.
The method can further include disposing the third material on a surface of the second material.
In one aspect, the invention features a method that includes disposing a noncrystalline layer of a second material on a surface of a first material. The second material is chemically compatible with a third material selected from the group consisting of superconductors and precursors of superconductors. The method also includes exposing a surface of the noncrystalline layer of the second material to at least two ion beams to texture the noncrystalline surface and to form a textured surface of the second material.
The third material can be, for example, a rare earth metal oxide superconductor or a precursor of a rare earth metal oxide superconductor.
The third material can contain, for example, YBCO or a precursor of YBCO.
The third material can be an acid (e.g., a halogenated acetic acid).
The can form a superconductor article having a critical current density of at least about 5xc3x97105 Amperes per square centimeter.
The layer of the first material can be noncrystalline.
The second material can be, for example, ceria, LaAlO3 or SrTiO3.
The first material can be, for example, YSZ or a nitride.
In anther aspect, the invention features an article that includes a substrate having a surface with a root mean square roughness of at least about 100 nanometers. The article also includes a layer of a first material supported by the surface of the substrate. The layer of the first material has a textured surface. The article further includes an epitaxial layer of a second material supported by the textured surface of the layer of the first material.
The first material can be an amorphous material.
The first material can be disposed on the surface of the substrate.
The first material can be a buffer layer material.
The epitaxial layer can be disposed on the textured surface of the layer of the first material.
The second material can be a buffer layer material.
The second material can be, for example, a superconductor material or a precursor of a superconductor material.
The article can have a critical current density of at least about 5xc3x97105 Amperes per square centimeter.
The second material can be, for example, YBCO or a precursor of YBCO.
In a further aspect, the invention features an article that includes a substrate having a surface with a root mean square roughness of at least about 100 nanometers. The article also includes a layer of a superconductor material supported by the surface of the substrate. The article has a critical current density of at least about 5xc3x97105 Amperes per square centimeter.
The article can have a critical current density of at least about 1xc3x97106 Amperes per square centimeter.
The layer of the superconductor material can be biaxially textured.
The layer of the superconductor material can be c-axis out of plane and biaxially textured in plane.
The article can further include a layer of a second material disposed between the substrate and the layer of superconductor material.
The the layer of the second material can have a textured surface that supports the layer of the superconductor material.
The layer of the superconductor material can be disposed on the textured surface of the layer of the second material.
The second material can be a buffer layer material.
The second material can be chemically compatible with the superconductor material.
The article can further include a layer of a third material disposed between the layer of the second material and the layer of the superconductor material. The layer of the third material can be chemically compatible with the superconductor material.
In one aspect, the invention features a system that includes a first ion beam source capable of emitting a first ion beam and a second ion beam source capable of emitting a second ion beam. The first and second ion beam sources are positioned so that when they emit the first and second ion beams, respectively, to impinge on a surface to texture the surface, the first ion beam is disposed at a first angle relative to a perpendicular to the surface and the second ion beam is disposed at a second angle relative to the perpendicular to the surface. The first and second ion beams are also disposed relative to each other at a third angle so that a crystal plane of the textured surface is oriented perpendicular to the textured surface.
The first angle can be different than the second angle.
The system can further include a third ion beam source capable of emitting a third ion beam. The third ion beam source can be positioned so that it emits the third ion beam to impinge on the surface to texture the surface. The third ion beam can be disposed at a fourth angle relative to the perpendicular to the surface, and the first and third ion beams are disposed relative to each other at a fifth angle so that a crystal plane of the textured surface is oriented perpendicular to the textured surface.
The system can further include a fourth ion beam source capable of emitting a fourth ion beam. The fourth ion beam source can be positioned so that it emits the fourth ion beam to impinge on the surface to texture the surface. The fourth ion beam can be disposed at a sixth angle relative to the perpendicular to the surface, and the fourth and third ion beams are disposed relative to each other at an angle so that a crystal plane of the textured surface is oriented perpendicular to the textured surface.
The invention can provide superconductor articles having a relatively high critical current density (e.g., coated superconductor articles having a relatively high critical current density, such as a coated conductor having a layer of superconductor material with biaxial texture in plane or a superconductor material with c-axis out of plane and biaxial texture in plane) without using a textured substrate (e.g., by using a noncrystalline substrate, such as a substrate having an amorphous surface or a polycrystalline surface).
The invention can provide superconductor articles having a relatively high critical current density (e.g., coated superconductor articles having a relatively high critical current density) without epitaxially growing a layer on the surface of a substrate.
The invention can provide superconductor articles having a relatively high critical current density (e.g., coated superconductor articles having a relatively high critical current density) with relatively few epitaxially grown layers (e.g., with only the layer of superconductor material being epitaxially grown).
The invention can provide relatively fast methods of growing a textured layer of material (e.g., a textured buffer layer of a superconductor article, such as a coated superconductor article).
The invention can provide methods of preparing a textured (e.g., highly textured) layer of material (e.g., a buffer layer of a superconductor article, such as a coated superconductor article) without growing the layer of material epitaxially.
The invention can provide methods of exposing a layer of material (e.g., a noncrystalline material, such as an amorphous material or a polycrystalline material) to ions to texture (e.g., highly texture) the material (e.g., to texture at least a region of the material adjacent a surface of the material exposed to ion texturing).
The invention can provide methods of preparing a superconductor article (e.g., a superconductor article having a relatively high critical current density), such as a coated superconductor article, in which a relatively stable layer (e.g., a layer of ceria (CeO2)) is used so that subsequent layer(s) (e.g., a layer of a superconductor material) can be incorporated (e.g., disposed) under different environmental conditions and/or after a relatively long period of time following formation of the layer (e.g., a buffer layer, such as a buffer layer having an ion textured surface) underlying the relatively stable layer.
The invention can provide methods of preparing a superconductor article (e.g., a superconductor article having a relatively high critical current density), such as a coated superconductor article, in which a layer of a superconductor material (e.g., YBCO) is disposed on a layer of a material (e.g., a layer of ceria) that is chemically compatible with the superconductor material and/or one or more precursor(s) of the superconductor material (e.g., a barium-containing precursor, such as a precursor containing BaF2). Generally, the layer of the chemically compatible material has a textured surface on which the layer of the superconductor material is disposed. The layer of chemically compatible material can be, for example, epitaxially grown, grown by ion beam assisted deposition, or prepared using ion texturing. Combinations of these methods can be used.
The invention can provide methods of ion texturing a layer (e.g., a layer of a superconductor article, such as a coated superconductor article) without concern for the ion to atom ratio used during ion bombardment.
The invention can provide methods of ion texturing relatively rough surfaces because the use of multiple ion beams can overcome shadowing effects.
The invention can provide methods of ion texturing that can overcome the natural growth orientation of the material of interest (i.e., the growth orientation of the material of interest in the absence of multiple ion beams). This can allow for the predetermined selection of the crystal plane that is oriented parallel to the ion textured surface.
The use of multiple (e.g., two, three, four, etc.) ion beams can reduce certain undesirable effects associated with ion beam divergence. In some embodiments, this can result in improved surface quality.
Features, objects and advantages of the invention are in the description, drawings and claims.